Last week, a bomb attack killed Sheik Abdul-Sattar Abu Risha, the charismatic leader of the coalition of Sunni tribes responsible for driving al Qaeda out of Iraq’s Anbar province.

While unlikely to affect the continued cooperation of the Anbar tribes with Gen. David Petraeus’ Coalition forces, it was a clear warning to other tribal leaders contemplating a similar alliance.

That is to say, don’t.

It bears remembering, however, that this is precisely the kind of al Qaeda thuggery that flipped Anbar to the Coalition’s side in the first place – and that was never clearer than in the case of Abu Risha himself.

The sheik had lost his father and three brothers to al Qaeda killers, giving his switch credibility with tribes suffering under the jihadists’ odious presence.

Under his lead – and encouraged by the promise of American constancy – the Anbar tribes last year started tipping off Coalition forces to the location of al Qaeda hideouts and weapons caches, while thousands of locals joined up with the Iraqi army.

Since then, the province has returned to some degree of safety and normalcy – so that attacks like the one that killed Abu Risha are now the exception instead of the rule.

Critics of the war have derided leaders like Abu Risha as “allies of convenience” – the implication being that they could easily switch sides again should circumstances change.

That’s true, of course: Deprived of American protection, few of the tribes could stand up to the violence of al Qaeda on the one side and the Iran-backed Shia militias on the other.

But, as Abu Risha showed, such alliances are founded on more than mere cynical calculation. The leaders of the Anbar tribes may be blatantly indifferent – if not actively hostile – to President Bush’s lofty “democracy” rhetoric, but they do care about the safety and prosperity of their people.

And as Gen. Petraeus understands, America’s long-term goals are only advanced as he gains Iraqi trust on that count, America is the only game in town.

There is little reason to canonize the good sheik, who – like everyone in Iraq these days – was a controversial figure. But he was an ally, one of many to whom America owes a debt of honor – and our continued support.